A report on Manchester code, Group coded recording and Non-return-to-zero

An example of Manchester encoding showing both conventions for representation of data
The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ(L), or polar non-return-to-zero-level code
Unipolar NRZ(L), or unipolar non-return-to-zero level
Non-return-to-zero space
Encoder for NRZS, toggle on zero
An example of the NRZI encoding, transition on 1
The opposite convention, transition on 0
Encoder for NRZI, toggle on one

For a given data signaling rate, i.e., bit rate, the NRZ code requires only half the baseband bandwidth required by the Manchester code (the passband bandwidth is the same).

- Non-return-to-zero

GCR is a modified form of a NRZI code, but necessarily with a higher transition density.

- Group coded recording

Manchester code was widely used for magnetic recording on 1600 bpi computer tapes before the introduction of 6250 bpi tapes which used the more efficient group-coded recording.

- Manchester code

Prior to 6,250 bpi tapes, 1,600 bpi tapes satisfied these constraints using a technique called phase encoding (PE), which was only 50% efficient.

- Group coded recording

The price of these benefits is a doubling of the bandwidth requirement compared to simpler NRZ coding schemes.

- Manchester code

Synchronized NRZI (NRZI-S, SNRZI) and group-coded recording (GCR) are modified forms of NRZI.

- Non-return-to-zero
An example of Manchester encoding showing both conventions for representation of data

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